A bicone is generally an antenna having two conical conductors, where the conical elements share a common axis, and a common vertex. The conical conductors extend in opposite directions. That is, the two flat portions of the cones face outward from one another. The flat portion of the cone can also be thought of as the base of the cone or the opening of the cone. The flat portion, or opening, of a cone is at the opposite end of the cone from the vertex or point of the cone. Bicone antennas are also called biconical antennas. Generally, a bicone antenna is fed from the common vertex. That is, the driving signal is applied to the antenna by a feed line connected at the antenna's central vertex area.
Positioning two cones so that the points (or vertices) of the two cones meet and the openings (or bases) of the two cones extend outward (opposite one another) results in a bowtie-like appearance. As such, some bicone antennas are called bowtie antennas.
Generally, bicone antennas support a wide bandwidth, but the low end of the operating frequency range is limited by the aperture size of the antenna. The relationship between aperture size and frequency operation is generally inverse. That is, operation at a lower frequency requires a larger bicone antenna. More specifically, a traditional bicone antenna requires an aperture size of about one half of the longest operating wavelength. The longest wavelength is related to the lowest operating frequency by the wave velocity relationship, “speed of light=wavelength×frequency” where the speed of light is approximately 300,000,000 meters per second.
Lower frequency operation requires bicone antennas that can be very large. These large antennas can have high material costs, high manufacturing costs, and high handling costs. Also, the larger antenna may be difficult to handle in the field, and may be prone to damage due to the large span of the conductive elements of the antenna. Traditional bicone antenna may also require external loading and cumbersome external feed assemblies.
Accordingly, there is a need in the art for an omni-directional bicone antenna where the aperture size can be reduced while maintaining a low VSWR (voltage standing wave ratio) over a broad bandwidth. There is also a need for a bicone antenna having compact and rugged design characteristics. There is a further need in the art for a bicone antenna that requires no external loading.